Bioluminescence imaging is a novel technique for visualizing biological processes within living animals. The cells or organism of interest are genetically modified to express luciferase, the enzyme that causes some insects, jellyfish, and bacteria to glow. Luciferase catalyzes a chemical reaction that generates light as one of its products. A highly sensitive camera captures this light and produces a semi-quantitative image reflecting cell trafficking, proliferation or gene expression in the living animal. Thus, by measuring light emission, one can monitor cellular or genetic activity and use the results to monitor the spread of a disease, or the effect of a new drug candidate in vivo. Only two companies (Xenogen, Alameda, CA and Photometries, Tucson AZ) currently manufacture equipment designed for bioluminescence imaging. Their approach uses a low f-number lens to collect about 0.2% of the photons emitted from the animal. We propose using a tapered fiber optic image conduit in place of a lens to increase photon collection efficiency. We hypothesize that this approach should increase the sensitivity of bioluminescence by capturing nearly all of the emitted photons. Improvements in the ability to detect signals in real time in live animals will ultimately result in better data, at lower cost, using fewer animals.